The present invention relates to methods useful in treating subterranean formations and, more particularly, to consolidating a potentially unconsolidated portion of a subterranean formation and minimizing the production of unconsolidated particulate materials such as formation fines and sand (referred to collectively herein as “particulate migration”). More specifically, the present invention relates to methods for introducing a consolidating agent into a subterranean formation and placing a sand control screen in at least a portion of a wellbore.
Without limiting the scope of the present invention, its background is described with reference to the production of hydrocarbons through a wellbore traversing an unconsolidated or loosely consolidated formation, as an example.
Hydrocarbon wells are often located in subterranean formations. that contain unconsolidated particulates (e.g., sand, gravel, proppant, fines, etc.) that may migrate out of the subterranean formation into a wellbore and/or may be produced with the oil, gas, water, and/or other fluids produced by the well. The presence of such particulates in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and/or reduce the production of desired fluids from the well. Moreover, particulates that have migrated into a wellbore (e.g., inside the casing and/or perforations in a cased hole), among other things, may clog portions of the wellbore, hindering the production of desired fluids from the well. The term “unconsolidated particulates,” and derivatives thereof, is defined herein to include loose particulates and particulates bonded with insufficient bond strength to withstand the forces created by the flow of fluids through the formation, which may cause the particulates to shift or migrate within the formation and/or into voids therein. Unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates in the subterranean formation, for example, proppant particulates placed in the subterranean formation in the course of a fracturing or gravel-packing operation. The terms “unconsolidated subterranean formation,” “unconsolidated portion of a subterranean formation,” and derivatives thereof are defined herein to include any formation that contains unconsolidated particulates, as that term is defined herein. “Unconsolidated subterranean formations” and “unconsolidated portions of a subterranean formation,” as those terms are used herein, include subterranean fractures wherein unconsolidated particulates reside within the open space of the fracture (e.g., forming a proppant pack within the fracture).
One method of controlling unconsolidated particulates in subterranean formations involves placing a filtration bed containing gravel (e.g., a “gravel pack”) near the wellbore to present a physical barrier to the transport of unconsolidated particulates with the production of desired fluids. Typically, such “gravel-packing operations” involve the pumping and placement of a quantity of particulate into the unconsolidated subterranean formation in an area adjacent to a wellbore. One common type of gravel-packing operation involves placing a screen in the wellbore and packing the surrounding annulus between the screen and the wellbore with gravel of a specific size designed to prevent the passage of formation sand. The screen is generally a filter assembly used to retain the gravel placed during the gravel-pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated particulates in the subterranean formation. To install the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a liquid carrier fluid, which is usually viscosified. Once the gravel is placed in the wellbore, the viscosity of the fluid may be reduced, and the fluid either flows into the formation or is returned to the surface. The resulting structure presents a barrier to migrating particulates from the formation while still permitting fluid flow.
It has been found, however, that a complete gravel pack of the desired production interval is difficult to achieve particularly in long or inclined/horizontal production intervals. These incomplete packs are commonly a result of the liquid carrier fluid entering a permeable portion of the production interval causing the gravel to form a sand bridge in the annulus. Thereafter, the sand bridge prevents the slurry from flowing to the remainder of the annulus which, in turn, prevents the placement of sufficient gravel in the remainder of the annulus.
In certain open hole completions where gravel packing may not be feasible, attempts have been made to use expandable sand control screens. Typically, expandable sand control screens are designed to not only filter particulate materials out of the formation fluids, but also provide radial support to the formation to prevent the formation from collapsing into the wellbore. It has been found, however, that conventional expandable sand control screens are not capable of contacting the wall of the wellbore along their entire length as the wellbore profile is not uniform. More specifically, due to the process of drilling the wellbore and heterogeneity of the downhole strata, washouts or other irregularities commonly occur which result in certain locations within the wellbore having larger diameters than other areas or having non circular cross sections. Thus, when the expandable sand control screens are expanded, voids are created between the expandable sand control screens and the irregular areas of the wellbore. In addition, it has been found that the expansion process undesirably weakens such sand control screens.
Additionally, in open hole completions, a stand alone screen may be used. Typically, stand alone screens may be used when the formation generally comprises a more uniform particle size distribution. However, when a formation comprises a wider range of particle sizes, a stand alone screen is not desirable because it is difficult to design a screen that will not plug. In addition, exposed shale also creates problems in these situations because the shale tends to slough when exposed to lower pressures, generating large volumes of fines that can flow into the annulus and plug the screen.
More recently, attempts have been made to install sand control screens that include telescoping screen members. Typically, hydraulic pressure is used to extend the telescoping screen members radially outwardly toward the wellbore. This process requires providing fluid pressure through the entire work string that acts on the telescoping members to shift the members from a partially extended position to a radially extended position. It has been found, however, that in substantially horizontal production intervals, the telescoping screen members may not properly deploy, particularly along the portion of the production string resting on the bottom surface of the wellbore. Failure to fully extend all the telescoping screen members results in a non uniform inner bore which may prevent the passage of tools therethrough.